Magnetization Dynamics in BaO·6Fe2O3 Single Crystals using Pulsed Magnetic Fields

Dynamic magnetization processes in BaO·6Fe2O3 single crystals in the easy direction are examined under rapidly varying high magnetic fields. We observe that for large values of dHa/dt (the rate of increase of the applied field) the derivative dM/dt of the sample magnetization as function of time shows a sharp structure with a maximum. A phenomenological interpretation is given, assuming that the magnetization change is only due to 180° Bloch wall displacement. In the initial stage of magnetization the number of domains remains constant and the wall velocity is directly related to the experimental results. This leads to an estimate of the viscous damping coefficient β which is found to depend very strongly on the value of the magnetic field, and is of the order of a few hundred cgs units when H reaches values comparable with the saturation magnetization Ms. Indeed in an effective field of several hundred oersteds, β appears to be several hundred times larger than it is in a field of a few oersteds. For instance, for dHa/dt=4.4 kOe/μsec and H=0.6 kOe, we obtain β=6.102 dyn·sec·cm−3.